| 摘要 |
PROBLEM TO BE SOLVED: To produce a finely pulverized polyvinyl acetal resin without cooling the reaction system to 0 deg.C or lower by carrying out the condensation of a part of polyvinyl alcohol and a carbonyl compound in an aqueous phase, lowering the temperature of the reaction system, then adding thereto the rest of polyvinyl alcohol, and adding the carbonyl compound in portions. SOLUTION: A carbonyl compound and polyvinyl alcohol in an amount of 80-99.5 wt.% of its total amount to be used are subjected to condensation in the presence of an acid catalyst while the reaction temperature is being kept at 20 deg.C or lower. The reaction temperature is then lowered, preferably to 0-5 deg.C, and before the precipitate of polyvinyl acetal appears, the rest (0.5-20 wt.%) of polyvinyl alcohol is added. Then, the carbonyl compound is added in portions. Preferably, polyvinyl alcohol having a degree of polymerization of 100-500 and a hydroxyl group content of 20-40 mol% is used.
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